Municipal and industrial wastes normally include materials that vary widely in physical properties and characteristics. Some materials commonly encountered in such waste include paper and wood pieces, plastics, wire, such as stainless steel shavings or wire, glass, metallic containers, tires, tire fragments, chips, semiconductor material, printed circuit boards, plastic or rubber covered materials including electric covered wires, factory waste material and any waste disposed of by consumers for instance, meat scrap such as beef, pork, fish and vegetable scrap.
There are numerous examples of methods for treating waste. In U.S. Pat. No. 3,595,488 Blakley et al. describe a waste treatment system using a pulverization technique with a rotary cutting or chopping device similar to a hammermill that fractures materials.
U.S. Pat. No. 3,555,996 to Schwarz et al. describes an apparatus and method for reducing the volume of commercial waste by pulverization using a hammermill arrangement in which the device employs a number of hammer sites for reduction of the size of the waste.
Nopper et al. in U.S. Pat. No. 4,290,988 describes a method for recycling cellulose fibers for use in cellulose fiber composites. The waste cellulose fiber is subjected to a dry grinding technique, using a grinder known in the art, to affect the chopping of waste paper product into a fibrous form for construction of fiber composites.
Kunogi et al. in U.S. Pat. No. 3,995,819 describe an apparatus and technique for reclaiming thermosetting plastics by pulverization involving hammermill type construction in which the hammer blades are made of an alloy of nickel chromium for high strength to impart the necessary force to shatter thermosetting plastics into a useful powdered and atomized form.
In U.S. Pat. No. 3,726,483 Kometani et al. define the process for making ultrafine polytetrafluoroethylene powders by using high speed impaction of nearly spherical particles in a collision zone, caused by high velocity air injection of the powder in 180.degree. opposed directions so that direct contact is made in the collision zone.
Brewer in U.S. Pat. No. 3,635,409 describes an integrated initiable waste system and method which uses wet and dry ball-mill grinding stages to reduce the particle size of floatable and non-floatable waste materials. The grinding is done in a ball-mill which is a modified type of hammering procedure.
In U.S. Pat. No. 4,607,796 Enikolopov et al. describe a process for pulverization of rubber and vulcanized rubber products using an extruder. In this invention the rubber material is subjected to a hot zone and then a cold zone and high compressive force is combined with the temperature differential which affects pulverization of the substance to form powdered material.
All of the above patents use either hammering to reduce the size of waste materials or thermally graded extruders with high shear force and compressive force to shatter the material into small parts because two roll milling is not effect to reduce the particle size to the mesh size designation and the energy cost for milling the excessive cycles or passes is prohibitive.
Due to the tendency of mill processes to agglomerate the particles to give larger masses and eventual sheets, as shown by the above cited patents, or the inability of milling to produce powders of less than 30 mesh economically, in recent years the practice of cryogenic processing with liquid nitrogen, etc. to give very fine particles has attracted a lot of attention unfortunately cryogenic processes are relatively costly and hazardous.
It is desirable to have a simplified and more efficient method for reducing the size of industrial and municipal waste independent of the composition of the waste. Also, powdered virgin rubber offer advantages in compounding rubber with compounding agents. This may be accomplished by subjecting the waste or virgin rubber to shear force in a compressive zone between two members, where at least one member is moveable and the material is prevented from sticking to the members by the lubricant or wetting agent and exits the zone essentially as a powder dry to the feel of the hands. The powders of this invention are dry and thus does not require drying, also, the fine particles of this invention can be compounded with finely divided compounded agents to give relatively economical produced masterbatches.